This is a multi-pronged metabolic and genetic epidemiologic study to examine two candidate genes (UCP3 and b3AR) implicated in energy metabolism. A total of 600 African American girls, aged 12-15 years, will be screened using buccal swabs as a non-invasive method of obtaining DNA, to determine their UCP3 genotypes as well as b3AR genotypes. An estimated 211 girls will be recruited, selected based on their UCP3 genotype, for measurements of resting energy expenditure and body composition (using dual energy X-ray absorptiometry [DEXA]) in a controlled setting of the Clinical Research Center at the Cincinnati Children's Hospital. Variation in resting energy expenditure will be examined across the genotypes of UCP3 with a large sample. The 2x3 design will allow the investigators to examine whether the effects associated with UCP3 variation are due to the UCP3 locus alone or due to the additive effect or interaction between UCP3 and b3AR. The study will help to elucidate the relationship between variation in two important candidate genes for energy metabolism, UCP3 and b3AR, and inter-individual variation in the levels of resting energy expenditure in this very high risk (for obesity) population.